From 147ed1bc807360c4c90784f975c24693cdd291d4 Mon Sep 17 00:00:00 2001
From: Ryan Buchner <ryan.buchner@arilinc.com>
Date: Tue, 12 Apr 2022 13:06:10 -0700
Subject: Skip storing in store_func if actually_store is false, add a fake
 store at start of AMO.

This includes skipping store in store_slow_path.

Is okay to skip the mmio_store part too, since the access_fault for mmio_failure will be caught on the actual store.

The ordering for the mmio_access fault is irrelevant since it will occur after the TW faults, and load faults are converted to store faults.

Will catch any faults from the access but won't perform a store.

Since store permissions can only be granted if read permissions exist,

any store faults will occur before or at the same time as a load fault.

Thus this store permissions check is sufficient for properly catching the faults in an Amo access TW.
---
 riscv/mmu.cc | 2 ++
 riscv/mmu.h  | 7 ++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/riscv/mmu.cc b/riscv/mmu.cc
index 6c7af21..40dccf0 100644
--- a/riscv/mmu.cc
+++ b/riscv/mmu.cc
@@ -172,6 +172,7 @@ void mmu_t::store_slow_path(reg_t addr, reg_t len, const uint8_t* bytes, uint32_
       throw *matched_trigger;
   }
 
+  if (actually_store) {
   if (auto host_addr = sim->addr_to_mem(paddr)) {
     memcpy(host_addr, bytes, len);
     if (tracer.interested_in_range(paddr, paddr + PGSIZE, STORE))
@@ -181,6 +182,7 @@ void mmu_t::store_slow_path(reg_t addr, reg_t len, const uint8_t* bytes, uint32_
   } else if (!mmio_store(paddr, len, bytes)) {
     throw trap_store_access_fault((proc) ? proc->state.v : false, addr, 0, 0);
   }
+  }
 }
 
 tlb_entry_t mmu_t::refill_tlb(reg_t vaddr, reg_t paddr, char* host_addr, access_type type)
diff --git a/riscv/mmu.h b/riscv/mmu.h
index deacbc4..fc6f950 100644
--- a/riscv/mmu.h
+++ b/riscv/mmu.h
@@ -153,10 +153,13 @@ public:
       reg_t vpn = addr >> PGSHIFT; \
       size_t size = sizeof(type##_t); \
       if ((xlate_flags) == 0 && likely(tlb_store_tag[vpn % TLB_ENTRIES] == vpn)) { \
+        if (actually_store) { \
         if (proc) WRITE_MEM(addr, val, size); \
         *(target_endian<type##_t>*)(tlb_data[vpn % TLB_ENTRIES].host_offset + addr) = to_target(val); \
+        } \
       } \
       else if ((xlate_flags) == 0 && unlikely(tlb_store_tag[vpn % TLB_ENTRIES] == (vpn | TLB_CHECK_TRIGGERS))) { \
+        if (actually_store) { \
         if (!matched_trigger) { \
           matched_trigger = trigger_exception(triggers::OPERATION_STORE, addr, val); \
           if (matched_trigger) \
@@ -164,11 +167,12 @@ public:
         } \
         if (proc) WRITE_MEM(addr, val, size); \
         *(target_endian<type##_t>*)(tlb_data[vpn % TLB_ENTRIES].host_offset + addr) = to_target(val); \
+        } \
       } \
       else { \
         target_endian<type##_t> target_val = to_target(val); \
         store_slow_path(addr, sizeof(type##_t), (const uint8_t*)&target_val, (xlate_flags), actually_store); \
-        if (proc) WRITE_MEM(addr, val, size); \
+        if (actually_store && proc) WRITE_MEM(addr, val, size); \
       } \
   }
 
@@ -192,6 +196,7 @@ public:
     template<typename op> \
     type##_t amo_##type(reg_t addr, op f) { \
       convert_load_traps_to_store_traps({ \
+        store_##type(addr, 0, false); \
         auto lhs = load_##type(addr, true); \
         store_##type(addr, f(lhs)); \
         return lhs; \
-- 
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